NEW ORLEANS -- A once-monthly injection of naltrexone (Vivitrol) kept more patients off opioids than did placebo, researchers reported here.

Action Points

Explain that a once-monthly injection of naltrexone (Vivitrol) appeared to decrease the use of opioids in patients who have had detoxification therapy for up to six months.

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered preliminary until published in a peer-reviewed journal.

NEW ORLEANS -- A once-monthly injection of naltrexone (Vivitrol) kept more patients off opioids than did placebo, researchers reported here.

After six months, the median percentage of opioid-free urine screens was 90% among those on the long-acting naltrexone compared with 35% on placebo (P=0.0002), David Gastfriend, MD, vice president of scientific communications for Alkermes, maker of the drug, reported during a press briefing at the American Psychiatric Association meeting here.

"We can offer a new treatment paradigm for opioid dependence that's not addictive and addresses the obstacle of poor patient adherence," Gastfriend said.

The more common treatment for opioid addiction is substitution therapy, typically with methadone, in which the medication binds to opioid receptors to mimic the drug's effect.

Naltrexone, on the other hand -- including the oral version -- is an opioid antagonist, which prevents opioids from binding to reception sites. While these kinds of drugs have less potential for addiction, they could cause withdrawal issues, researchers say.

Extended-release naltrexone is currently approved for treating alcohol dependence in adults who have completed detoxification treatment.

So to investigate the safety and efficacy of the once-monthly injectable dose of naltrexone, the researchers conducted a 24-week, placebo-controlled, multicenter phase III study of 250 patients with opioid dependence.

All patients had been off opioids for at least seven days before being enrolled in the trial. They were randomized to either 380 mg of extended-release naltrexone or placebo, with 126 and 124 in each group, respectively.

The majority of the patients were male, and their mean duration of opioid dependence was 10 years.

The primary endpoint was response profile based on the rate of urine test results negative for opioids during the last 20 weeks for the 24-week treatment period.

Aside from the significantly better median percentage of opioid-free drug screens, the researchers also found significantly better outcomes for a host of secondary endpoints.

They saw significantly better retention (P=0.004) and less self-reported opioid use (P=0.003) among those on the drug, as well as a lower incidence of physiologic opioid dependence (P=0.017).

There was also a greater reduction in VAS-craving score from week eight to 24 among those on the extended-release drug (P<0.001).

"We saw a rapid decline in craving level," Gastfriend said. "The placebo group never goes below baseline, and bumps up as they leave the study. For the naltrexone group, (craving reduction) began in the first week, progressively decreased through the eighth week, and was significantly different from baseline every week until the end of study."

There were no significant between-group differences in the incidence of clinical adverse events and no severe adverse events or premature discontinuation due to the drug, the researchers said.

Gastfriend added that the most common clinical adverse events were nasopharyngitis and insomnia.

"We believe these are compelling clinical data," Gastfriend said. " This may provide patients and physicians with a new treatment option -- a nonaddictive, once-monthly treatment for opioid dependence."

He cautioned that it's not intended to "take over existing treatments" -- it's just another tool in the armamentarium.

Petros Levounis, MD, who was not involved in the study, said it's "encouraging to have more options in our treatment of opioid dependence." Levounis is director of the Addiction Institute of New York at St. Luke's and Roosevelt Hospitals, in Manhattan.

But he cautioned that compliance could be an issue. "How many patients," he said, "are willing to have that shot every month?"

Still, he called it "a shame" that pharmacologic interventions for drug addictions are not as widely used as they could be.

"For some opioid [addictions], we've come up with some particularly good medications," he said, "and we should use them."

Gastfriend added that the FDA recently designated the new drug application for extended-release naltrexone in opioid addiction as a priority review.

The study was supported by Alkermes. Gastfriend is an employee of the company.

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